The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to the older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. With the development and deployment of the 5G system (5GS), the 5GS allows multiple access, including 3GPP accesses and non-3GPP accesses, to the network. With the optimization of the network design, many improvements have developed over the evolution of various standards. With the development of the 5G system (5GS), the base station/gNB would support enabling reduced UE bandwidth capability within a wideband carrier and enabling reduced UE power energy consumption by bandwidth adaptation.
The main function of the Session Management (SM) for 2G/3G systems or Evolved Packet System (EPS) SM (ESM) for 4G systems is to support Packet Data Protocol (PDP) context or EPS bearer handling of the user terminal. Upon receipt of the registration request message, the network may reject the request with a cause code. For different cause codes, the network may provide a retry mechanism for the user to resend the SM/ESM request if certain conditions are satisfied. However, for some specific cause codes, the UE is not allowed to apply the retry mechanism and resend another SM/ESM request unless the UE is switched off or the USIM is removed. As a result, those cause codes create probably permanent rejection in providing data service to the user. The legacy system, such as the evolved packet system (EPS), specifies protection mechanism to protect the UE against a denial of service attack against mobile terminal from a fraudulent network. With the development of the 5GS, the UE could access the 5GS core network (CN) via 3GPP accesses and non-3GPP accesses. The protection mechanism against a denial of service attack against mobile terminal from a fraudulent network does not exist for the 5GS and requires considerations of the multiple access characteristics of the 5GS.